Reduced offspring production in bark beetle Tomicus piniperda in pine bolts baited with ethanol and alpha pinene, which attract antagonistic insects

Bolts of Scots pine, Pinus sylvestris L., attacked by the bark beetle Tomicus piniperda (L.) were baited with ethanol and alpha-pinene to attract antagonistic insects and thereby enhance their detrimental effects on the production of bark beetle progeny. Unbaited and caged bolts were included in the experiments as controls. Attraction of beetles to the bolts and subsequent emergence were estimated using traps. Six phloem-feeding species (potential competitors of T. piniperda) and four predatory species were caught in significantly higher numbers at the baited bolts than at the unbaited ones. The number of offspring and the productivity of T. piniperda were four to seven times higher in unbaited bolts than in baited bolts. Exclusion of other insects, by using cages, resulted in a nine-fold increase in the number of T. piniperda offspring per square meter and productivity (offspring per egg gallery) compared with unbaited, exposed bolts. Hylurgops palliatus (Gyll.) (Scolytidae) and Rhagium inquisitor (L.) (Cerambycidae) attacked both the baited and unbaited bolts, whereas Acanthocinus aedilis (L.) (Cerambycidae) and Pytho depressus (L.) (Pythidae) reproduced almost exclusively in the baited ones. Large numbers of larvae of Thanasimus (Cleridae) and Rhizophagus (Rhizophagidae) emerged from both the baited and unbaited bolts. Adults of Plegaderus vulneratus (Panzer) and Cylister linearis (Er.) (Histeridae) emerged almost exclusively from the baited bolts. The low progeny production of T. piniperda in the baited bolts was attributed largely to the influence of adults of Rhizophagus and Epuraea (Nitidulidae), and larvae of Thanasimus and A. aedilis.